Replacement/upgraded accelerator pump jets? By glavey (Read 2,906 times)

[glavey]

Are there different sizes of accelerator pump jets out there? I have a feeling that the accel. pump/jet in the carb on my scoot isn't giving the engine enough gas when I snap the throttle open.

[Alleyoop]

What kind of carb do you have? Does you carb have a pump on it that when you twist the throttle it squirts a little gas into the venturi, or a none pump CV carb?

On the carbs the only jets you can change to different sizes are the PILOT JET and the MAIN JET.
Are you talking about the PILOT JET?
Alleyoop

[glavey]

My carb has an accelerator pump on it. It looks just like this one:



The accelerator jet I am talking about is the one you can see in this picture, just behind the rubber cover:


I don't mean the pilot jet, I have tried changing those to larger and smaller sizes. If I go up in size, the engine is flooded at idle; if I go down in size, the engine runs lean at idle.

[Alleyoop]

Ok, so you have a cv carb with a pumper, but there is no jet in there all it does is it pushs a diagram at the bottom where it looks like a saucer and squirts a little bit of gas into the venturi. All you can do is adjust the part on the throttle to squirt with less twist of the throttle or when more twist of the throttle to push the rod down and squirt gas in. It is just one squirt and that is all.

So what is it that your complaining about when you twist the throttle does it bog or what? Don't forget you have a 130QMB 50cc motor not many ponies that it puts out and it has to move the weight from a standstill. So it takes a bit for the rpms to come up and start moving the weight forward.

Now what it may be is that your rpms are not building high enough and it may be that the weights in the variator or a little on the heavy side. Lighter weights will give you more rpms and quicker take offs if that is what your looking for.
Alleyoop

[glavey]

When I twist open the throttle quickly from idle with the engine at normal operating temperature and the enricher fully extended, the engine will, for about 1/4 of a second, sound normal; as if it is going to accelerate as you would predict it would. After that the engine bogs for about 1/2 to 1 second, then the rpms climb and the scoot accelerates as you would expect.

I'll see if I can get a video demonstrating what I mean uploaded some time today if the weather cooperates.

I'm quite sure it isn't the variator weights, the engine bogs the same when it is on the center stand with and without weights installed.

[cyborg]

it very well be getting too big of a shot of gas,,and also as a side it's a cv carb so there's always a delay,,,one of the big reasons i switch all my bikes to the TM series mikunis as soon as i can,,instant response,,,i even found a tiny one to run on my et4 vespa,,,it cured all my carburetion woes

[Alleyoop]

Try turning the Fuel ratio screw 1/4 Counter clockwise and see if it the bog clears up, if it get worse then turn it 1/4 clockwise at a time and after Each 1/4 turn try it. Bogs are usually not enough fuel and to much air at that point in time.

In your case it is not your CVT it is your fuel delivery just needs a little carb adjustment.
Alleyoop

[jerryscript]

Have you adjusted the pumper spring? I'm referring to the curved piece of metal that is pressed by the throttle assembly to pump the accelerator. Bend it or straighten it to get the most effect from the pump. You may just need a bit more spray.

When you turn the throttle, you are opening up the butterfly, allowing more air in, and temporarily decreasing the vacuum. Less vacuum means less fuel being pulled through the jets. The accelerator pump delivers a short spray of fuel to compensate, allowing the engine to build up vacuum and pull more fuel.

[glavey]

it very well be getting too big of a shot of gas,,and also as a side it's a cv carb so there's always a delay,,,one of the big reasons i switch all my bikes to the TM series mikunis as soon as i can,,instant response,,,i even found a tiny one to run on my et4 vespa,,,it cured all my carburetion woes

I have thought about that quite some time ago, back when I didn't know too much about my scoot. I decided against it because it would make troubleshooting and asking for help difficult because I wouldn't be using the standard carburetor that comes with these engines.

However, having owned my scoot for about 5 years I think I might be able to do it. But for the immediate future, I'll stick with the CVK carb.

Try turning the Fuel ratio screw 1/4 Counter clockwise and see if it the bog clears up, if it get worse then turn it 1/4 clockwise at a time and after Each 1/4 turn try it. Bogs are usually not enough fuel and to much air at that point in time.

In your case it is not your CVT it is your fuel delivery just needs a little carb adjustment.
Alleyoop

I tried tuning the carb by turning the fuel adj. screw CW and CCW with every idle jet including 30, 32, 33, 35, 38, and 40. The only idle jet that doesn't flood the engine at idle (out of the ones listed above) is the 30; it's the one I have in the carb now.

Have you adjusted the pumper spring? I'm referring to the curved piece of metal that is pressed by the throttle assembly to pump the accelerator. Bend it or straighten it to get the most effect from the pump. You may just need a bit more spray.

When you turn the throttle, you are opening up the butterfly, allowing more air in, and temporarily decreasing the vacuum. Less vacuum means less fuel being pulled through the jets. The accelerator pump delivers a short spray of fuel to compensate, allowing the engine to build up vacuum and pull more fuel.

I have adjusted the spring that pushes the plunger. When the carb was new, the spring was about 1-2mm from the plunger when the throttle was at idle. I adjusted it so that there is just a hair's breadth between the spring and the plunger (I used a feeler gauge between the two, the same one that is used for adjusting the valves).

I would like to be able to completely (temporarily) remove or disable the accel. pump to see how the engine behaves without it. I know I could bend the spring all the way up, but I'm afraid if I do that too many times it will break.

[glavey]

The weather was finally good enough to get a video of the problem.

The scoot was warmed up from a several-mile ride in the video and both times I was giving it full throttle.

[Alleyoop]

Yes you have a slight hesitation on take off, Try richen the fuel mixture 1/4 counter clockwise, If it gets worse then go Leaner turn it CLOCKWISE but only turn it 1/4 at a time and try it after each 1/4 turn.

[glavey]

I tried that, no luck. I'm using a #30 idle jet at the moment; I get the highest idle speed (with the hesitation) at about 2 1/8 turns out. If I turn the adj. screw more CCW the idle drops, but the hesitation remains, the same thing happens when I turn the adj. screw CW; the idle drops and the hesitation remains.

I have tried putting in a #32 idle jet, but that floods the engine even with the adj. screw all the way in.

[jerryscript]

Is the hesitation right at takeoff, or as you turn the throttle more while accelerating? If the latter, trying raising the needle by lowering the clip one notch our adding a washer if it doesn't have a clip.

[Alleyoop]

Yep Jerry is on it if the FUEL RATIO SCREW does not help then it is time time to RAISE the MAIN JET NEEDLE by 1 notch by moving the clip DOWN 1 slot on the needle.
Alleyoop

CLICK ON THE PICTURES TO EXPAND THEM:

[glavey]

Ok, I'll try that the next chance I get.